Epitaxial superconducting thin films are sometimes desirable. The best epitaxial high-temperature superconducting thin films are obtained on only a few substrates such as SrTiO.sub.3, LaAlO.sub.3, MgO, and yttria-stabilized zirconia (YSZ). Although such superconducting films have excellent superconductive properties, none of those substrates are ideal for use in applications of, e.g., microwave devices, because of a high loss tangent and a high dielectric constant with LaAlO.sub.3 and a poor lattice match for MgO and YSZ.
One approach to this problem has been to use a buffer or intermediate layer between the bulk substrate and the superconducting film. On substrates such as silica and sapphire, such buffer layers have been found necessary to prevent chemical reactions between the superconductor and the substrate. Among the buffer layers that have been previously tried are PrBa.sub.2 Cu.sub.3 O.sub.7-x, SrTiO.sub.3, LaAlO.sub.3, MgO, YSZ, and Y.sub.2 O.sub.3. Problems with most previous intermediate layers have included their multi-elemental composition thereby resulting in composition control during deposition, and a poor lattice match with either the substrate or the superconducting material. While MgO is a simpler intermediate layer, it also suffers from a large lattice mismatch with the superconductive films.
Accordingly, it is an object of this invention to provide an intermediate layer for superconductor-coated substrates, such an intermediate layer having chemical and structural compatibility to superconductors such as YBCO.
It is a further object of this invention to provide an intermediate layer-coated substrate that can then be coated with a superconductive film of, e.g., YBCO, such a substrate having chemical or structural compatibility to the superconductor.
Still another object of the invention is to provide a method of insulating between adjacent superconductive junctions by placing an intermediate layer of a intermediate layer such as CeO.sub.2 between the adjacent superconductive junctions.